The present invention relates to a compact tribology tester for testing the wear of interfacing surfaces and lubrication properties.
In general, tribology testers are used to study the design, friction, wear, and lubrication of interacting surfaces which are in relative motion. Such interfacing surfaces may include bearing surfaces, gears, or the like. There are several types of tribology testers including testers using test blocks and a rotating pin, pin-on-disk testers, four ball testers, and friction testers.
An example of the type of tester that uses test blocks and a rotating pin is described in U.S. Pat. No. 2,110,288 to Cornell and includes mounting the pin to a drive motor for rotation therewith. A pair of test blocks are supported in the tester in contact with the rotating pin. As shown in FIG. 7 of the Cornell reference, a load is applied to the test blocks and thus the pin by plugs which threadedly engage supports in which the test blocks are mounted. As the plugs are threaded into the supports, the load upon the test blocks and thus the pin is increased. The test blocks are provided with concave portions in which the pin is received so as to ensure a contact between the blocks and the pin. The position of the test blocks may be adjustable so that the contact between the test blocks and pin may be varied. The test block and pin assembly is placed into a tray filled with lubricant. The motor drives the pin to rotate against the testing blocks in the lubricant such that the wear of the material of the test blocks against the material of the pin and the properties of the lubricant can be observed.
A second type of tester 170 is illustrated herein, in FIGS. 6 and 6A, and includes pressure chamber 172 in which test specimens 174 and 176 are mounted. Pressure chamber 172 allows the environment to be a pressurized fluid rather than being exposed to ambient air or simply submersed in lubricant. Further, chamber 172 may be adapted so that the fluid may be heated. Shaft 178 is mounted in chamber 172 by bearings 180 and seal 182 with test specimen 174 mounted to one end thereof. Test specimen 176 is mounted to an internal end of movable shaft 184 of gimbal assembly 186. Shaft 184 extends through a sidewall of pressure chamber 182 requiring seal 194 between the shaft and sidewall. Hence, this tester is non-hermetic. A load is applied to external end 188 of shaft 184 in the direction of arrow 190 which in turn causes shaft 184 to pivot slightly about seal 194, and test specimen 176 to be upwardly loaded against test specimen 174. Magnetic drive assembly 192 is located at the end of shaft 178 opposite to test specimen 174 and is provided to rotatably drive shaft 178. Rotation of shaft 178 causes rotation of test specimen 174 against stationary test specimen 176.
Several problems exist with prior versions of the above-identified testers. One such problem with the pin and test block type tester of Cornell is that the pin and test block assembly is merely submersed into an open tray of lubricant. Therefore, operating conditions encountered in a pressurized vessel, such as a compressor, are not achieved.
A problem with above-identified tester 170 mounted within pressurized chamber 172 is that the maximum pressure within chamber 172 is limited due to potential leakage between specimen shaft 184 and the sidewall of chamber 172 across seal 194. Therefore, sustained high-pressure operating conditions, where pressures may reach 3000 psi, cannot be reliably reproduced. Additionally, the load is applied to test specimens 174 and 176 externally of chamber 172 via specimen shaft 184. A problem with external loading of the specimens is that a significant amount of space is required to accommodate shaft 184. Further, seal 194 may impart a force, or torque, on shaft 184 which may be a function of the internal pressure within chamber 172, for example. This force may be difficult to account for in the test results, and thus the test results may be altered.
It is desired to provide a self-contained, compact tribology tester for testing the wear of interfacing surfaces and properties of the lubricant in a compressor under hermetic operating conditions.
The present invention provides a compact tribology tester device which is located within a hermetically sealed vessel. The device includes a test pin which slidably engages a pair of test blocks, each block being mounted at the end of a lever arm. The lever arms are pivotally attached, with a spring located between the arms. The spring creates a force which, through the blocks, is exerted on the pin.
The pin is mechanically coupled to a rotating shaft mounted in the vessel. The shaft is magnetically coupled to drive means, such as a motor, located outside of the vessel. The testing device is mounted on a support which is secured in the vessel such that the pin shaft of the device is aligned with the motor. Operation of the motor rotatably drives the shaft to cause rotation of the pin between the blocks. The temperature and pressure of a testing medium, such as an oil and refrigerant mixture, located in the vessel can be varied in order to simulate the operating conditions of a hermetic compressor so that the wear between interfacing surfaces and properties of the lubricant during operation may be analyzed.
Particular embodiments of the present invention provide a testing apparatus including a hermetically sealed vessel in which a tribology tester is completely mounted. A drive means is located externally of the hermetically sealed vessel and operatively engaging the tribology tester.
Particular embodiments of the present invention further provide a testing apparatus having a hermetically sealed vessel, and a tribology tester mounted completely therein. A drive means is located externally of the hermetically sealed vessel. A tribology tester is mounted completely within the hermetically sealed vessel. The tribology tester includes a test block assembly having a block and a pin, at least one of which is a test specimen. The drive means is operatively engaged with the pin to drive the pin. The tribology tester also includes means for loading the block against the pin which is located completely within the hermetically sealed vessel.
Particular embodiments of the present invention also provide a tribology tester having a test block assembly including a pair of blocks and a pin. The test blocks are located on radially opposite sides of the pin. The test block assembly further includes at least one test specimen where at least one of a test block and the pin is the test specimen. The tribology tester also includes means for applying a substantially equivalent and constant load between each block and the pin during wearing of the test specimen.
Particular embodiments of the present invention also provide a method of testing material properties including selecting at least one test specimen of a material to be tested, the test specimen being a block or a rotating pin; mounting a tester into a vessel; placing the block and the rotating pin in engagement; applying a load between the block and the rotating pin; hermetically sealing the vessel; filling the hermetically sealed vessel with a pressurized fluid test medium; and rotating the pin with drive means located outside the hermetically sealed vessel.
One advantage of the present invention is that more realistic operating conditions can be simulated with the tribology tester device being located in a hermetically sealed vessel.
Additionally, an advantage of the present invention is that by providing the tribology tester within a hermetically sealed vessel, tribology testing under very high pressures, such as those experienced with refrigerants such as, for example, carbon dioxide, may be achieved.